Integrated circuit (IC) technology, applied to imaging, is revolutionizing that field. Semiconductors can be used to represent an image as an electrical signal. Charge coupled devices (CCDs) are the most significant commercial IC technology to date. However, when compared with CMOS technology, there are many advantages to producing CMOS image devices.
CMOS is a less expensive technology; CMOS employs fewer mask layers and is a more mature fabrication technology with greater commercial volume. CCD technology complexity causes lower fabrication yield. One of the main benefits of employing CMOS technology, compared to CCD, is the ability to include image-processing elements on the same substrate as the imaging circuitry.
On a monolithic semiconductor IC, with a surface coincident to an optical focal plane, photosensitive elements are employed in pixels that are arranged in an array of rows and columns. The basis for the pixels of CMOS technology is a photosensitive diode. In an active pixel arrangement each pixel photodiode is buffered from the shared readout components by an amplification stage.
IC image sensors of existing technologies provide video style output. In one example, such a sensor receives master clock input. The sensor derives data sample, line, and clocks from this master clock. These clocks, which correspond to pixel, row, and column, control the sampling rate of the imaging array. The pixel data of such a sensor is output at the same rate as it is sampled. The derived clocks are output as well to synchronize the data output. The result is a stream of synchronized pixel intensities comprising a video frame.
This output is incompatible with the data interface of commercial microprocessors, without the use of additional glue logic. A commercial microprocessor data interface consists of address and control output signals and data input/output signals. This configuration allows the processor to randomly access any word of data in memory by asserting various addresses.
In an image acquiring computer system based on such a sensor and such a processor, additional interface circuitry to respond to the sensor clock outputs to sample the video information, and to make this video data available in the memory space of the processor. Optionally, this interface circuit may include interrupt signals to the processor, and enough memory space for a number of pixels.
Such additional circuitry diminishes the benefit of a single substrate that integrates sensor and processing elements. The CMOS technology optimum cost benefit is not reached.
Therefore, there is a need for an interface which may be integrated with the imaging array which a system processor can access to directly receive imaging data.